How do I change back to normal default view from user perspective view?
Just hold middle mouse button and drag to rotate the view.

The 5 on your Numpad switches between perspective and orthographic view.

Numpad 0 switches into Camera view.

Numpad 1  Front View

Ctrl Numpad 1 Bottom View

Numpad 3 Right View

Ctrl Numpad 3 Left View

Numpad 7 Top View.

Ctrl Numpad 7 Bottom View